1. Field of the Invention
The present invention relates to a magnetic recording medium used for a magnetic recording apparatus such as a magnetic disk apparatus and, more particularly, to a magnetic recording medium having improved durability.
2. Description of the Prior Art
In a magnetic recording medium such as a hard magnetic disk for performing high-density recording, a metal magnetic thin film medium formed by, e.g., plating, sputtering, or evaporation, has been used in place of a conventional coating type medium using a coating type magnetic film containing a magnetic powder and a binder.
When a recording/reproducing operation is performed with respect to a hard magnetic disk, in general, a CSS (contact start stop) system is used. In the CSS system, the disk is rotated at a predetermined speed, so that a very small air layer is formed between a magnetic head and the magnetic disk, and a recording/reproducing operation is performed in this state.
In the CSS system, the head is physically in contact with a surface of the magnetic disk in a stop mode. At the start and end of rotation, the head and the magnetic disk move relative to each other in a contact and friction state. The head and the magnetic disk surface are worn by the friction at this time. When the head is brought into contact with the magnetic disk surface at high speed during a recording/reproducing operation, and large friction occurs between the head and the magnetic disk surface due to the presence of very small dust, the head or the magnetic film is often damaged. In particular, in the metal magnetic thin film medium, since the friction coefficient of the metal magnetic film is high, and the thickness of the film is small, the above problem is conspicuous.
Therefore, in order to achieve corrosion resistance and lubricity of an upper portion of the metal magnetic film, a magnetic recording medium, in which an inorganic oxide protective film such as an SiO.sub.2 film is formed on a magnetic film directly or through a first protective film, and a liquid lubricant (e.g., fluorine oil; perfluoroalkylpolyether) is coated on an upper portion of the inorganic oxide protective film, has been conventionally used (e.g., Japanese Patent Laid-Open No. 61-160834).
An attempt has also been made to increase the coupling force between a lubricant and the inorganic oxide protective film by using a liquid lubricant having a polar group or functional group (e.g., Japanese Patent Laid-Open Nos. 61-208618 and 61-220120).
In the conventional magnetic recording medium on which a liquid lubricant is coated, however, the protective film is insufficiently coupled to the lubricant. Therefore, when CSS is repeated, the effect of the lubricant is gradually reduced, and the friction force is increased. As a result, sufficient wear resistance and damage resistance cannot be obtained. In addition, when the lubricant having the polar group or functional group is coated, the protective film is strongly coupled to the lubricant. However, the coupling force between the lubricant molecules is also increased. Therefore, an adhesion force between the head and the magnetic disk is increased, and the static friction force often exceeds the drive force for the motor of the magnetic disk medium.